In so-called “Resin Transfer Molding” methods (RTM methods), complex composite fiber plastics with a high volumetric fiber content are produced by impregnating dry semi-finished fiber products with resin. The RTM method is also referred to as resin injection method and represents a complete process that makes it possible to achieve close manufacturing tolerances with respect to component weight, volumetric fiber content and component dimensions. In the technical realization of this method, a dry semi-finished fiber product is placed into a heated tool that is divided into two parts and brought in functional contact with a low-viscosity resin under pressure. During this process, the resin flows through the fiber layers and, after having impregnated the fibers, is discharged through ventilation openings.
In the RTM method, a lower mold may be provided with fiber mats and, if applicable, additional parts (for example, foam cores). After the lower mold is closed with an upper mold, the closed molds are subjected to a vacuum and the resin is injected by a pump. A composite component is then manufactured under the influence of heat, wherein said composite component can subsequently be removed from the mold after it is opened.
Composite fiber plastics manufactured with the aid of the RTM method can be utilized in numerous fields, e.g., as structural components in the manufacture of automobiles or in the aircraft and spacecraft industry. Examples of fiber-reinforced plastic products include mountings for a rudder unit of an aircraft, paneling elements for passenger cars as well as elevated roof and wind deflection systems for motor trucks.
Consequently, the RTM method makes it possible to manufacture composite components. Depending on the tool design and the material selection, it is possible to manufacture components with their final dimensions.
Different variations of the RTM method have been devised. In one resin injection method, structural components of fiber-reinforced plastic are produced by placing dry semi-finished fiber products into a mold cavity, subsequently closing said cavity and injecting the liquid resin. The closed molding results in defined dimensional and positional tolerances of the components on all sides. The term closed molding refers to a solid (for example, metallic) cavity comprising at least two mold halves that are called the upper cavity and the lower cavity.
In known devices for manufacturing a component by means of the RTM method, one encounters the problem that the tool may shrink onto the component during the cooling process. The component can only be removed from the mold without being damaged by utilizing rotary inserts (cores and wedges) that are inserted between the trough and the cover on one hand and the material for manufacturing the component on the other hand. After this manufacturing method, resin residues need to be laboriously removed from the tool as well as the inserts. This results in significant wear of the tool and the inserts.
This wear lowers the quality of the component being manufactured with respect to its dimensional stability, surface quality and edge structure. One consequence of this is a high reject rate.